The present invention relates to high energy density capacitors and the dielectric materials used therein. It particularly relates to dielectric materials of polymerized (alpha-substituted)acrylate monomers or use in a thin film capacitor, such as a polymer multilayer capacitor.
Capacitors, which basically include two electrodes separated by a dielectric material, are used in a wide variety of electrical applications to accumulate and store an electrical charge. The development of electronic devices and circuits of reduced size has led to a need for significantly smaller capacitors having increased capacity per unit volume and high temperature capabilities.
Thin polymer films offer significant potential to produce smaller capacitors with increased capacity per unit volume. Such capacitors could therefore reduce the size of implantable devices, such as defibrillators, which currently use relatively large aluminum electrolytic capacitors in which the dielectric is aluminum oxide. Such large capacitors have an energy density of about 2 Joules/centimeter3 (J/cm3), which leads to capacitors of about 15 cm3. Smaller and lighter weight capacitors having higher energy densities (e.g., at (e.g., at least about3 J/cm3) would provide significant advantage in decreasing the size of implantable devices.
One type of small, high energy density capacitor is referred to as a polymer multilayer (PML) capacitor. Examples of such capacitors are described, for example, in U.S. Pat. No. 4,499,520 (Cichanowski), U.S. Pat. No. 4,490,774 (Olson et al.), U.S. Pat. No. 4,954,371 (Yializis), 5,097,800 (Shaw et al.), and U.S. Pat. No. 5,032,461 (Shaw et al.). They are typically made by a vapor deposition process in which a polymerizable compound is vapor deposited onto a substrate and polymerized to form a polymer film. The polymerizable compounds are typically polymerized using electron beam or ultraviolet radiation. The polymer films are then typically metallized by either sputtering or vapor depositing a metal, such as aluminum. These processes (vapor coating, polymerizing, and metallizing) are repeated until the desired number of layers has been achieved.
Although there are a number of polymeric dielectric materials known for use in high energy density capacitors, such as PML capacitors, there is still a need for a wider variety of such materials that have the potential to produce smaller capacitors with increased. capacity per unit volume. There is a particular need to produce small high energy density capacitors for use in high voltage defibrillators.
A number of patents and other documents have been reviewed in which polymeric dielectric materials are disclosed. Also, a number of patents have been reviewed in which capacitors, particularly PML capacitors, are disclosed. Although not admitted as prior art, these documents are listed among others in Table 1 below.
All documents listed in Table 1 above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of Preferred Embodiments, and Claims set forth below, many of the devices and methods disclosed in these documents of Table 1 may be modified advantageously by using the teachings of the present invention.
It is a primary object of this invention to provide compounds that can be used to form polymeric dielectric materials, particularly thin dielectric films, in high energy capacitors, such as polymeric multilayer capacitors. This and other objects will be clear from the following description.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art with respect to capacitors. Specifically, the present invention addresses the need for significantly smaller capacitors having increased capacity per unit volume as a result of the development of electronic devices and circuits of reduced size. This has been accomplished by developing new organic polymeric dielectric materials for use in high energy density capacitors, i.e., capacitors that have an energy density of at least about 3 J/cm3.
In comparison to known capacitors, various embodiments of the present invention may provide one or more of the following advantages: improving the ability of the capacitor to store charge as a result of increasing the dielectric constant; improving the energy loss of the capacitor as a result of decreasing the dissipation factor of the dielectric material; and improving the electrical breakdown of the capacitor as a result of increasing the dielectric strength of the dielectric material. As a result of one or more of these advantages, small, high energy density capacitors can be made.
Some embodiments of the invention include one or more of the following features: a high energy density capacitor that includes an organic polymeric dielectric material having a dielectric constant of at least about 7; a high energy density capacitor that includes an organic polymeric dielectric material having a dielectric constant of at least about 10; a high energy density capacitor that includes an organic polymeric dielectric material having a dissipation factor of no greater than about 0.10; a high energy density capacitor that includes an organic polymeric dielectric material having a dielectric strength of at least about 250 V/xcexcm; and a high energy density capacitor that includes an organic polymeric dielectric material formed from polymerizable alkyl (alpha-substituted)acrylate monomers having at least one dipole group, wherein when the monomers are polymerized, the dipole group is attached to the main polymeric chain through a heteroatom-containing linking group.
A preferred embodiment of the present invention is a high energy density capacitor comprising an organic polymeric dielectric material having a dielectric constant of at least about 7; wherein. the organic polymeric dielectric material comprises polymerized alkyl (alpha-substituted)acrylate monomers having at least one dipole group; wherein when the monomers are polymerized, the dipole group is attached to the main polymeric chain through a heteroatom-containing linking group. Such high energy density capacitors can be included in a variety of implantable devices of a relatively small size, such as implantable defibrillator devices.